Standard or Daylight Time?
We should take this opportunity to discern how arbitrary the laws are for a subject we interact with so much: the “When”
The above map displays the current summer solstice sunset times (about June 21), the longest day in the year, with Daylight Savings Time in effect.
I love looking at this map I easily found online, just four decades after I manually filled in a map of the lower 48 with these half-hour intervals after figuring out the formula and checking it against polar and other times reported in the nautical almanac, the best source I could find in the whole UC Berkeley math and astronomy library. If you know trigonometry and a couple of basic astronomical facts which I won’t bore you with until a TMI (too much information) sidebar below, it’s doable.
A side benefit of this visual aid is the bonus of pondering what its mathematical beauty conveys (if you’re like me) in addition to the actual effect the decision of time zone placement has on the lives of those you interact with. Where to begin (once you recover from this graphic diversity, if you’re new to it)? How about with just what is rational here?
No, that adjective is no patronizing trap from someone with a particular agenda. I mean that I’m inviting you to consider just what makes sense about the state of affairs I’m about to impart to you, regardless of your opinion on changing our clocks.
According to the USA Today website on March 3:
While a state needs congressional approval to stay on daylight saving time all year, staying on standard time all year only requires a state law. The state also would need to notify the U.S. Department of Transportation it will not be observing daylight saving time, the DOT said in an email.
Note that neither congressional approval nor state law is contingent on any chaos relative to neighboring states that might result. While congress might well be expected to take this into account, apparently Mississippi — which is completely surrounded by Central Time Zone states like itself — could run on Standard Time when its neighbors in all directions are an hour ahead!
You might deem it extremely unlikely that any state would do such a thing. If so, can you rest assured that no state (whatever your opinion of them) has inflicted comparable absurdity — or worse — on any party, in any issue? Feel free to consider any real or imagined reports pertaining to alleged political acts.
Furthermore, if anyone can assure that common sense prevails, why the DOT requirement? Or is this just an archaic requirement from a prior century when the time of far-flung destinations might not have been readily determinable for a given date?
If it’s not worth the process of amending outdated laws, people should be advised of them. Maybe not because they should expect repercussions from afoulment of them, or simply for amusement at the expense of diligent public servants, but to fine-tune their minds to the hijinks of experts in scary propaganda on other matters.
And Mississippi’s just an extreme example. Under the standard time rule, any state could choose to disregard Daylight Savings Time and therefore be an hour earlier than states west of it in the same zone. The closest we have to that confusion right now is knowing the order of polling place closure times on the days a president is elected.
Aside from the circadian problems with changing the clock, common arguments in favor of DST involve energy conservation and increased evening recreation, whereas a strong opposition concerns the safety of children in the morning.
This map shows the number of days each year that parts of the country would have the sunrise after 7 a.m. if Daylight Savings Time continued from March until November (and were added for Arizona). This and the top map remind us of how we might think that hourly time zones are sufficient to equalize different regions that actually have the sun rise and set up to an hour or more apart—and how we take that for granted.
Or we could have half-hour time zones like eastern Canada, Australia, Iran, and India (among others). Or like China, we could legislate that the whole large country use the same zone. Should that result in the current western zones gaining more hours or losing fewer than in the east, we can be glad that most historians now believe protests attributed to 1752 when England lost eleven days by adopting the Gregorian calendar are urban myths.
To keep the scope of this article reasonable, I’ll forgo the possibility that such caution won’t be tempted under the rubric of “never let a crisis go to waste” to convert us to metric time, about which there is plenty of material elsewhere — but presumably nothing about disrupting people’s sense of rhythm by counting 100,000 seconds per day instead 0f 86,400.
Obviously, there’s no satisfying everyone, but — especially when a society considers the inconvenience of a change that is intended to be permanent — we should be glad this is one public policy where the elegant use of maps reminds us that places can be very differently affected. Would that such stark differences could overcome hyperbole in other areas…or at least call attention to the possibility of it? (Beyond rise and set times, at higher latitudes twilight takes longer, especially when the days are long; more on this below).
And there is a reason why the fall and spring time changes aren’t symmetrical with the equinoxes; an irregularity in the earth’s orbit causes the sun to rise and set up to a half hour earlier in November than in February, as any almanac will show you. This difference is known as the aquation of Time. So any opposition to DST shouldn’t be blamed on your aesthetic for balance.
“TMI” sidebar (contains spoilers)
The vertical line in the figure below is at a 23.5 degree angle from the earth’s axis. Not coincidentally, this is both the latitudes of the tropics and the distance of the Arctic and Antarctic Circles from the poles, but the earth is only at this angle relative to the sun at the solstices. On June 21, imagine the sun to the right of the earth in the diagram, while it would be at your head during the northern hemisphere’s spring equinox, just as the stars the earth faces in space during your night change during the year.
When I was a kid and read that the day was 23 hours and 56 minutes long, I assumed it meant that 24 hours was rounding or something like that. It really means that since the earth’s rotation is a little over 360 days, it takes about four minutes a day to rotate about one degree more so that the same longitude faces the sun as it did a day earlier. In fact, the aforementioned equation of Time results from the earth’s orbit being elliptical, because the earth is closest to the sun on January 2, so it orbits the sun faster while its rotation remains constant, thereby pushing the solar time up to 30 seconds later each day around then (image below) — but this is irrelevant to length of day itself.
You may have seen a globe with a figure eight that depicted the sun’s apparent movement (an analemma), its width conveying the half-hour difference between November and February (a smaller difference exists at the other end of the year, as seen below).
The angle between the vertical line and the axis might be thought of as the center of triangle OEP (orbital plane-equator-pole, below), which shows that the higher the latitude, the more the “excess” line of latitude would be in daylight, just as the majority of the Tropic of Cancer is to the right of the vertical. Since we are viewing a sphere head-on, the vertical distance between such latitude rings would diminish with increasing latitude even as their lit proportion increased — until the Arctic Circle would be completely lit.
The combination of increasing latitude and shrinking latitude rings would mean the amount of daylight increases proportionately with the latitude’s sine and cosine. And as angle OEP (relative to the sun) decreases with the sun’s declination away from the solstice, the greater light the latitude receives diminishes. And since a higher latitude must be reached to attain full daylight, the cosine of the declination also plays a role. So the root of the formula was the arcsine of [the tangent (sine divided by cosine) of the latitude times the tangent of the declination].
While the reader may confirm their perceived ineptitude trying to follow all that, I accept imperfection at explaining it, having mastered it so long ago. Anyway, I’m glad I didn’t have the temptation to turn to the back of the Internet back then.
But comparing those to random place and date rise and set times (especially at high latitudes in June) revealed a couple more considerations:
The sun is considered to rise and set when the visible edge meets the horizon, not its center, and the visible width of the sun is just over half a degree: 32 minutes of arc (thirty-two sixtieths of a degree). But there an even stronger and stranger factor:
All objects in space visible through the atmosphere enjoy our gaze longer because of refraction by just over half a degree, 34 minutes (and it can change under unusual circumstances). Taken together, this and the prior paragraph can result in a meaningful difference, especially at high latitudes.
So the “additional” set or rise time base is 50 minutes of arc (34 plus half of 32). Since an astronomical body appears to move one degree (60 minutes of arc) through space in 4 minutes, 50 arc minutes would require 50/15 minutes of time. Which would have to be added twice to account for the timee between an object’s rise and set times (even the moon). And that’s only on the equator, where objects appear to rise and set vertically. Both of the above factors cause the sun to move away from the vertical by a location’s latitude. At latitude 60 degrees, this means such movements would take twice as long as the times would have to be divided by the latitude’s cosine of 0.5 (that is, multiplied by two).
Think of speeded-up sun movements you may have seen in a few seconds on TV over the years in commercials and on shows such as Breaking Bad, as the angle is much more obvious than in real life. And during twilight the time lengthens as the altitude increases. As you might be able to imagine, the angle of movement reduces as its glow approaches the pole during long days — to the point that the sky never fully darkens in June very near the Canadian border (I’ll disregard possible aircraft antics here). Who says the tropics get more sun?
And when someone says the time zone boundary in west Texas is ideally placed through the Guadalupe Mountains because of their gorgeous sunsets, you can agree that it was a great decision because it means people can see it twice a day — at least if you don’t want to alert others by speaking more rationally than they might, if you’re blessed with such companions!
